Hydraulic brake



` Aug. l0, 1937. l H. D. GEYER HYDRAULIC BRAKE Fi'led- Jan 2 1936 Patentedl Aug. ll0, 1937 HYDRAULIC BRAKE Harvey D. Geyer, Dayton, hio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 2, 1936, Serial No. 57,106L

Claims.

This invention relates to sealing means for a piston reciprocable in a cylinder. It has been designed more particularly as a seal for the piston of the wheel cylinder of a hydraulic brake sys- 5 tem. It is, of course, useful in many other relations.

The invention may be described as an improvement for use in place of the flexible cup sealing means commonly used with a piston having a sliding t in its cylinder and also as an improvement over other known forms of sealing means such as rubber cups peripherally secured to the cylinder and expansible axially by uid pressure to move the piston engaged by the cup.

The object of the invention is to provide a seal between the cylinder and piston wherein leakage to or from the cylinder is prevented.

Another object is to provide such a seal wherein the piston movement may not damage the sealing means.

Another object is to provide a bond between the sealing means andthe piston and cylinder which shall not fail during the life of the vehicle with which the device is used.

Other objects and advantages will be understood from the following description.

In the drawing accompanying the invention, Fig. 1 shows a vertical section through a brake drum having brake shoes therein with my novel shoe expanding means associated therewith.

Fig. 2 is a top plan view, partly in transverse section, substantially on line 2 2 of Fig. l.

Figs. 3, 4 and 5 are three transverse sections of modified forms of sealing connections between the cylinder and the piston reciprocable therein.

`Referring to the drawing, numeral II is used to designate a wheel-carried drum adapted to be engaged by shoes I3, said shoes being anchored in any way preferred.

Between the adjacent ends of the shoes I3 is a wheel cylinder I5 secured .in any convenient manner as by fastening means I4 to a fixed backing plate I6. A reciprocable piston to be more fully described is located in each end of cylinder I5.

Between the pistons the cylinder wall has' an aperture I1 adapted to receive a connection I9 at the end of a conduit 2| connecting with any preferred form of master cylinder. At 23 is a bleed opening closed by a plug 25, this provision being conventional and designed to permit the Venting of trapped air.

The two pistons are marked 2'I. Their external diameter is appreciably less than the internal diameter of the cylinder. Between the pistons and the adjacent shoe ends are thrust pins 29.

(Cl. (5U-54.6)

These pins may have bifurcated ends 3I to pre-r vent rotation relative to the shoes and, at their opposite ends, are rounded to be received in similar shaped pockets 33 in the pistons. Releasing spring means are marked by numeral 35. There 5 is shown no provision for adjustment of the distance between the pistons and the shoes to accommodate for lining'wear. Any preferred adjustment may be used if desired.

The invention is concerned particularly with l0 the sealing means between the piston and the cylinder, the idea being to provide such a seal as will effectively prevent the escape ofthe hydraulic fluid and also prevent the admission of air as sometimes occurs in the case of conventional slidl5 ing pistons. Iprefer to use an annulus 31 of noncompressible flexible material such as rubber. 'Ihis annulus is bonded to the external surface of the piston 2'I and to the internal surface of a metallic ring 39, which latter is press-fitted into the 20 cylinderv I5. I make the bond by vulcanizing the rubber annulus to the piston and to the ring.

Several types of bond are herein shown illustrating successive steps leading to that shown in Fig. 1 and Fig. 2 which I now believe to represent 25 the best embodiment of my invention.

In my earliest steps leading up to the disclosure herein, I used a rubber ring corresponding in general to that marked 31 herein, which ring I vulcanized to a piston periphery and to the inner 30 wall of a metallic ring resembling in a, general way ring 39. I then subjected the piston to a coining step to expand it radially and reduce it l axially. This had the effect of stretching the rubber circumferentially, compressing it radially, A35 and effecting an elongation axially. In use, reciprocating movements of the piston produced a rolling action in the rubber annulus, the strained condition of the annulus serving of course to restore the parts to the initial position. 40

It was found advisable after testing these first vulcanized rubber cups to improve the bonded connections. The first step in the improvement is shown by Fig. 3. In this form the steel ring 39 is formed with a reduced diameter region 4I 45 on its outer surface at one end. The rubber ring 31 is formed with an extension 43 fitting the inner surface of the end of the ring 39', and the extension 43 surrounds the end of the ring 39' and fills the space 4I. This arrangement gives a 50 greater area of contact and a better bond between the ring 39 and the rubber. Also, when the ring 39' is pressed into the cylinder, the rubber within the region 4I is held between the cylinder and ring, thus aiding in holding the rubber 55,

' at rest.

from separation from the ring and cylinder. This step in the development was found to improve very considerably the bond between the metallic ring and the rubber annulus.

To afford a better bond between the piston and the rubber ring, a larger diameter piston was used than in the form just described. The larger piston is shown by Fig. 4. It reduces the radial distance of the annular space between the piston 21" and the ring 39.` 'I'he rubber is then vulcanized to the two metal parts as before. When the piston is coined to expand it radially and reduce its axial length, the rubber is subjected to greater compression than with the smaller piston of Fig. 3 since the reduced volume of the annular space into which the rubber is expanded as compared with that ofFig. 3 is out of proportion to the reduction in volume of the rubber ring in the two cases prior to the coining of the piston. Also the circumferential grip of the rubber on the piston is increased owing to the use of the. larger piston.

While these two steps improved the bond both with the piston and the metallic ring, a further' improvement was made by adding somewhat to the mass of the rubber as at 45, ysee Fig. 5. In

this form the inner end of the piston 41 is made ilat, the peripheral wall formed as shown, and the other side has a wider and deeper ilared opening 50 than in the earlier forms. This deeper opening has the effect of locating the point of engagement with the pin 29 deep down in the piston and preferably beyond its mid portion to the end of maintaining the axis of piston movement co' incident with its normal axis of the piston when When this sort of piston is coined as before, there is formed a bead 49 as shown, which bead aids in holding in the rubber. The bead reduces the radial distance between the piston and the ring 39' whereby any tendency of the 40 rubber to be squeezed through the annular space adjacent the bead is effectively resisted and the danger of damage to the rubber Vannulus or to its bond with the metal surfaces is avoided. 'Ihis form showed considerable improvement. In life 45 tests it was the rubber itself between the bonds which failed rather than the bonded region.

In the form shown in Fig. 1 and Fig. 2 substantially the same type of bonding is used. The mass 'of rubber is considerably increased not only 50 by a greater radial thickness as at 5I but by reducing the axial length of the metallic ring- 39 whereby the rubber extension of the metallic ring, so to speak, is of considerable length. This final form in which the invention is'embodied is believed to be so free from weakness in the rubber itself and in the bond between the rubber and the metallic surfaces as to ensurefreedom from leakage of the hydraulic medium or from the entrance of air to the hydraulic system that it may serve throughout the life of the vehicle on which it is used. The expedients fre- Said member in spaced relation thereto, a rubber annulus located therebetween and bonded to both, said rubber annulus havinga part integral therewith extending axially to and beyond the end of said spaced ring and bonded to both internal and external faces of said end.

2. The invention dened by claim 1 said rubber annulus also having a radial bead at the end thereof opposite said integral extension.

3. A cylinder, a ring press-fitted into said cylinder, a piston reciprocable in said cylinder, a rubber annulus between said piston and ring and bonded to both, said rubber annulus having a part integral therewith bonded to the end of said ring on both the external and internal faces thereof, whereby the outer part of said rubber annulus is held between the ring and cylinder.

4. A cylinder for hydraulic brakes, a ring-pressy tted therein, a piston reciprocable in said cylinder and ring, a rubber annulus *bonded to said piston and ring, said ring having an external recess at one end and said rubber annulus extending axially beyond the ring, lling said recess and bonded to the external wall of the ring within the recess.

5. A cylinder, a ring press-fitted therein, a piston reciprocable in said cylinder, a. rubber annulus between said ring and annulus and bonded to both, said piston extending axially beyond one end of said ring and said rubber annulus lling the space between said piston extension vand `said cylinder.

HARVEY D. GEYER. 

